The present invention relates to an optical head and optical drive device which allows execution of the reproduction or recording of an optical disc.
JP-A-02-236827 (Patent Document 1) exists as a prior art in the present technological field. In JP-A-02-236827, the description has been given as follows: “There is provided an optical reproduction device equipped with a diffraction-based track recording medium. The present optical reproduction device generates positive and negative different-signs' signals at the forward end and backward end of a diffraction element. In this way, the present device makes it possible to detect the diffraction element regardless of length of the diffraction element. The present device also makes it possible to detect even a kind of diffraction element whose length is equal to whose width. The present device is also applicable to the case of the reflection-based reading of information stored in a substrate medium”.